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Brain-imaging with fMRI can't be used with individuals with a cochlear implant. The electromagnetic fields originating in a structural or functional MRI investigation (static magnetic fields, static gradients, switched gradients, and radio frequency pulses) interfere with cochlear implants. These critical fields may induce heat resulting in damage to the surrounding tissue of the internal device, evoke voltages that may damage the internal portions of the device, or dislodge the surgically implanted device through force and torque on the magnetic parts of the implant. The internal magnet of the implant causes artifacts in the structural MR image (up to 6 cm in circumference) and it is partially demagnetized, resulting in reduced functionality.
Although the cochlear implant manufacturers continue to develop equipment upgrades to allow cochlear implant users to obtain structural MRIs for medical emergencies and diagnostic needs, the techniques cannot be used to assess the response of the central auditory system to electrical stimulation associated with functional MRI. Guidelines for magnetic resonance imaging safety are available at the Web sites of cochlear implant manufacturers. SPECT and PET, however, offer several advantages for assessing cortical activations in cochlear implant users since they do not evoke the harmful consequences seen in functional MRIs.
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